Respiratory syncytial virus (RSV) is the leading cause of severe respiratory illness in infants and young children and is the major cause of infantile bronchiolitis (Welliver (2003) J Pediatr 143:S112). An estimated 64 million cases of respiratory illness and 160,000 deaths worldwide are attributable to RSV induced disease. In the United States alone, tens of thousands of infant hospitalizations are due to infections by paramyxoviruses, such as RSV and parainfluenza virus (PIV) (Shay et al. (1999) JAMA 282:1440-1446). Severe RSV infection occurs most often in children and infants, especially in premature infants. Underlying health problems such as chronic lung disease or congenital heart disease can significantly increase the risk of serious illness. RSV infections also can cause serious illness in the elderly, individuals with chronic pulmonary disease and immunocompromised adults, such as bone marrow transplant recipients.
Several approaches to the prevention and treatment of RSV infection have been investigated, including vaccine development, antiviral compounds (ribavirin), antisense drugs, RNA interference technology, and antibody products, such as immunoglobulin or intravenous monoclonal antibodies. Intravenous immunoglobulin (RSV-IGIV; RespiGam®) isolated from donors and a monoclonal antibody, palivizumab (SYNAGIS™), have been approved for RSV prophylaxis in high risk children. A vaccine or commercially available treatment for RSV, however, is not yet available. Only ribavirin is approved for treatment of RSV infection. In order to be effective for treatment of RSV infection, high doses, frequent administrations and/or volumes of antibody products, such as RSV-IG and palivizumab, are required due to low specificity. Further, the use of products, such as intravenous immunoglobulin, is dependent on donor availability. Accordingly, there exists a need for additional agents for the prevention or treatment of RSV infections.